Dell proprietary PSU repair [SOLVED]

[wraper]

Check if there is power on pin 4 of CL2181, referenced to GND, (pin 10)

[spilihps]

I dont Think i can get a probe to that pin when it is mounted on the mainboard.
However, i may be able to see in my notes if that pin is connected directly(via some resistor or something) to a pin on the mainboard.
I know that after having the cl2181 board out several times, there is no open Connections on it. i will see what i can come up with

[wraper]

solder a wire to it.

[spilihps]

Hello.

Wraper, thank you very much for your help.

I get ~1.6v on it. And it jumps to ~3.8 just when first turned on.. (it could be more if the DMM is not fast enough)

Edit: ~ is approximately, not AC

[wraper]

too low, start searching from there.

[spilihps]

Alright,

So it is connected directly from the board, to the Q104 transistor (That i replaced, the OPTOcoupler one)
The collector of that one is connected via a resistor and a zener to a larger "island" that is interconnected via jumpers, to another large "island" that have one leg of the main cap.
This is also connected (to the left of the board instead) to the source of the large FET.
Does this make any sense?

[spilihps]

Alright. So, tracing some further. that is directly connected to one of the legs on the little board with the thermistor and the relay i was talking about.

Does it give us any hints?

Edit: will desolder the zener and test it OC

Edit2: The zener might have fooled me in circuit
It measures ~0.150v both ways and likewise ~150ohm both ways?

How can one identify it. The only readable text on it is "16" the rest have been under the manufacturing glue(i think)

[wraper]

likely it is 16V rated. post a photo

[spilihps]

Here is a Picture.

It measures 3,45mm in lenght

[wraper]

to which parts it is connected?

[spilihps]

Lets see if i can take this by text!

CL2181 pin 10 - Emitter on Q104 (npn transistor)

Collector on Q103 - > resistor -> one side of zener parallell with one of the optos
The other side of the zener is connected back to the cl2181 board(not sure of what cl2181 pin) and parallell with source of large mosFET

Make any sense?

[wraper]

Should be zener, 16V also seem to be about right. Find some 16V replacement. You also can use a 2 lower voltage zeners in series to achieve needed voltage.

[spilihps]

Great I will see if I can find one. Don't have any on hand though

It seems to be SOD-80, and 16v what about zener-resistance?

[wraper]

It seems to be SOD-80, and 16v what about zener-resistance?

It this case any 500mW zener should work fine. Most likely it is used only for overvoltage protection of the IC. Normally it shouldn't clamp anything IMO.

[spilihps]

Alright!

Will get one in a couple of days, you think that it could be causing this problem as it is right now?

[wraper]

yes, it seem to short the power of CL2181.

[spilihps]

Great!

Hard to wait for the diode thuough, haha!

I do have another PSU-board that have zeners on it in the correct package. However, they are colorcoded like brown,blue,blue, no clue about the voltage or anything

[Voodoo 6]

My Gateway 960 had an odd ball power supply, mainly for SCSI termination (3.3 vdc) to the SCSI back-planes. Here is what I did, I obtained a nice power supply and cut the connectors off the old power supply and wired them in. If the dell has a special plug going to the motherboard just snip it off and connect the wires accordingly. The other plugs are usually the same 12 / 5 volts dc going to the drives. Its fun to explore but digging out all that old potting is never fun. The original Compaq's use to have the low profile power supplies and getting the originals were fairly expensive, but we did manage to find a 3rd party vendor. 

[spilihps]

yes, it seem to short the power of CL2181.

wraper, SUCCESS!!!!

i found two 8v zeners laying around, hooked them up! It started right up! I almost dont believe it!
Also now the relay clicked. It didnt do that before.

Just one last question, i measured the 12v rail, and actually it seems a bit low. It comes in at 11.5v. Now this is completely unloaded with just the DMM hooked up. Maybe it have something to do with that?

Edit: Hooked up a HDD as load and it went up to 11.8 so i guess we are alright?

[wraper]

Congratulations!
Output voltage is independent from that. It is compared against reference on the secondary side. Primary side only "knows" if it needs to increase or decrease PWM duty cycle depending on the signal from optocoupler. Also as there are multiple voltage rails with shared regulation, it is not perfect and voltage can change depending on how much each rail is loaded.

[spilihps]

Again, thank you for all your help!

Then everything seem to be ok! I will order the right SMD zener and put it in!

What do you think may have caused a failure like this? Seem to be kind of common.

Is it the FET that die of age, or is there something else causing it?

[wraper]

The first part to fail, most likely, was either mosfet or CL2181, all other things were consequences of everything going haywire. Reasons can be different, like hidden manufacturing fault or some transient in the mains, overheating under heavy load.

[spilihps]

Alright! Good to know. Well see how long it will run then.

The CL2181 is a suspect since that one is found online in different circuits but it failed in the same way.

Ive checked the main filter cap ESR, and it seem to be fine atleast..

[wraper]

The CL2181 is a suspect since that one is found online in different circuits but it failed in the same way.

Main suspect is mosfet as power parts fail the most often. When it fails, PWM controller IC goes bust in most cases too, regardless of it's model.

[spilihps]

Alright. Yeah, it have both a thermalpad, and it had dried up thermalpaste, so ive removed the old and replaced it with new. It may very well have overheated the FET actually when thinking of it..